Temporary attach article and method for temporary attach of devices to a substrate

ABSTRACT

A temporary attach article of a first component to a second component which includes a first component having a first volume of a fusible material; a second component having a second volume of fusible material; and the first and second components being joined together through the first and second volumes of fusible material, wherein the first volume of fusible material has a melting point higher than a melting point of the second volume of fusible material so that the first and second components may be joined together without melting of the first volume of fusible material and wherein the second volume of fusible material is 5 to 20% of the first volume of fusible material. Also disclosed is a method for temporary attach of devices to an electronic substrate.

BACKGROUND OF THE INVENTION

The present invention relates to the attachment of semiconductor devicesand the like to an electronic substrate and, more particularly, relatesto the temporary attachment of semiconductor devices and the like to anelectronic substrate for testing and burn-in.

The method of attaching semiconductor devices to an electronicsubstrate, for example a ceramic material, by controlled collapse chipconnection (C4), also known as flip chip attach, is well known in theart. In the C4 method, an array of solder balls is formed on the surfaceof the semiconductor device. The solder balls are typically composed ofhigh melting point solder, for example 97 weight % lead, 3 weightpercent tin (97/3), at an approximate pitch of 10 mils. The solder isreflowed at a temperature of about 350° C. to join the semiconductordevice to the electronic substrate. There can be one semiconductordevice per electronic substrate, known as a single-chip module (SCM), ormultiple semiconductor devices per electronic substrate, known as amulti-chip module (MCM).

After manufacture of the semiconductor devices, they are tested forelectrical continuity. More recently, semiconductor devices undergo“burn-in” which is the preliminary operation of the semiconductor deviceto detect early failure of the functioning of the semiconductor device.There is a growing need in the microelectronics industry for known gooddie (KGD), which are semiconductor devices that have been tested andburned-in and are known to be good prior to sale or installation. It isalso desirable that semiconductor devices used to populate an MCM beknown to be good prior to being placed on the MCM, so that it is notnecessary to reflow the MCM several times to replace semiconductordevices that may be bad.

In order to produce KGD, one method is to test the semiconductor deviceon a ceramic carrier to which the KGD has been soldered. The carrier, orelectronic substrate, can be a standard single-chip carrier, whichenables the semiconductor device to be tested and burned-in. A keyattribute of this process should be the ability to remove thesemiconductor device from the electronic substrate without damaging thesemiconductor device or the C4 solder balls on the semiconductor device,so that the semiconductor device can be used in its final application.It is a simple matter to mount a semiconductor device on a conventionalelectronic substrate by the C4 connection method and test and burn-inthe semiconductor device. However, the matter is complicated whenremoval of the semiconductor device is attempted without damaging the C4solder bumps on the semiconductor device so that the semiconductordevice may be used on another electronic substrate.

Today, this problem has been addressed by using a ceramic electronicsubstrate with reduced solderable pads on the top surface of theelectronic substrate. Using a C4 pad on the electronic substrate whichis approximately 1.5 mils in diameter, as opposed to the standard padsize of 5.5 mils, enables a semiconductor device to be joined to theelectronic substrate by reflow of the C-4 solder balls, tested,burned-in and subsequently cold-sheared off of the electronic substrate.The effectiveness of this solution requires a reduced area solderableconnection on the electronic substrate.

Aimi et al. U.S. Pat. . 5,237,269, the disclosure of which isincorporated by reference herein, provides a reduced area solderableconnection on the electronic substrate by masking the solderable areawith an overlay which is made of a non-wettable material to which solderwill not adhere. Holes are provided in the overlay such that arestricted connection may be made between the C-4 solder balls and theunderlying solderable area of the electronic substrate. After testing,the C-4 solder balls are sheared from the electronic substrate and thenreflowed to reshape them for subsequent use.

Various solutions have been proposed for joining semiconductor devicesto electronic substrates. Chong et al. U.S. Pat. No. 5,535,936, thedisclosure of which is incorporated by reference herein, discloses amethod of applying low temperature solder in a fine pitch pattern on aprinted circuit board for the purpose of attaching (permanentlyapparently) a semiconductor device to a printed circuit board. As notedat column 2, lines 18-22, approximately 20-80 cubic mils of solder areneeded on the printed circuit board for a reliable joint.

Tsukada U.S. Pat. No. 5,488,200, the disclosure of which is incorporatedby reference herein, discloses a method for reusing SCM or MCMsubstrates by end milling the chips and underfill off the top surface ofthe substrate and establishing a planar surface of residual C4 solder towhich a new chip can be joined using low temperature solder.

Baker U.S. Pat. No. 4,739,917, the disclosure of which is incorporatedby reference herein, discloses high temperature solder mounds depositedon conductive pads on the substrate which function only as mechanicalguides for the various lead configurations of the components. Then, lowtemperature solder is deposited and reflowed over the mechanicallyanchored high temperature mounds and component leads to make the joint.

It would be desirable to be able to have a process for temporaryattachment of the semiconductor device to an electronic substrate foruse in test and burn-in, and subsequent removal of the semiconductordevice without damaging the C4 solder balls on the semiconductor device,which is low cost and easily manufacturable.

Accordingly, it is a purpose of the present invention to have a processfor temporary attachment of the semiconductor device to an electronicsubstrate for use in test and burn-in, and subsequent removal of thesemiconductor device without damaging the C4 solder balls on thesemiconductor device.

It is another purpose of the present invention to have such a processwhich is relatively low cost and easily manufacturable.

It is yet another purpose of the present invention to have an articlefor the temporary attachment of the semiconductor device to anelectronic substrate for use in test and burn-in, and subsequent removalof the semiconductor device without damaging the C4 solder balls on thesemiconductor device.

These and other purposes of the present invention will become moreapparent after referring to the following description considered inconjunction with the accompanying drawings.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is a temporaryattach article of a first component to a second component comprising:

a first component having a first volume of a fusible material;

a second component having a second volume of fusible material;

the first and second components being joined together through the firstand second volumes of fusible material, wherein the first volume offusible material has a melting point higher than a melting point of thesecond volume of fusible material so that the first and secondcomponents are joined together without melting of the first volume offusible material and wherein the second volume of fusible material is 5to 20% of the first volume of fusible material.

According to a second aspect of the invention, there is a method oftemporarily attaching a first component to a second component, themethod comprising the steps of:

preparing a first component having a first volume of fusible material;

preparing a second component having a second quantity of fusiblematerial, wherein the first volume of fusible material has a meltingpoint higher than a melting point of the second volume of fusiblematerial and wherein the second volume of fusible material is 5 to 20%of the first volume of fusible material;

joining the first and second components through the first and secondvolumes of fusible material without melting of the first volume offusible material.

According to a third aspect of the present invention, there is a methodof temporarily attaching a first component to a second component, themethod comprising the steps of:

preparing a first component having a first volume of fusible material;

preparing a second component having a second volume of fusible material,wherein the first volume of fusible material has a melting point higherthan a melting point of the second volume of fusible material andwherein the second volume of fusible material is 5 to 20% of the firstvolume of fusible material;

joining the first and second components through the first and secondvolumes of fusible material without melting of the first volume offusible material;

electrically testing and burning-in the first component; and

separating the first and second components.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel and the elementscharacteristic of the invention are set forth with particularity in theappended claims. The Figures are for illustration purposes only and arenot drawn to scale. The invention itself, however, both as toorganization and method of operation, may best be understood byreference to the detailed description which follows taken in conjunctionwith the accompanying drawings in which:

FIG. 1 is a schematical representation of a first embodiment oftemporarily attaching a first component to a second component.

FIG. 2 is a schematical representation of a second embodiment oftemporarily attaching a first component to a second component.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings in more detail, and particularly referring toFIG. 1, there is shown a first embodiment of the present invention. Itis desired to temporarily attach first component 10 to second component12 for electrical testing and burn-in. First component 10 will usuallybe a semiconductor device such as an integrated circuit die but couldalso be a passive device such as a capacitor. Second component 12 willbe an electronic substrate suitable for receiving the first component 10and will usually be a ceramic or glass-ceramic substrate but could alsobe a printed circuit board.

First component 10 consists of body 14 having all the usual internalcircuitry and ball 16 of fusible material. As is well known to thoseskilled in the art, there will usually be an array of fusible balls 16but only one is shown here for clarity. Fusible ball 16 has been formedon body 14 by conventional techniques. Fusible ball 16 typicallycomprises a lead/tin solder. One typical composition is 97 weight % leadand 3 weight % tin which has a melting point in excess of 300° C.

Second component 12 consists of body 18 having internal circuitry, partof which is shown as via 20. On top of via 20 is reduced area pad 22 onwhich has been deposited a quantity of fusible material 24. As anexample, via 20 may be 5 to 6 mils in diameter and may be made frommolybdenum or copper while reduced area pad 22 is smaller in dimensions,e.g., 2 to 3 mils in diameter, and may be selectively plated nickel ornickel/gold. Fusible material 24 may be tin, indium, an alloy of leadand tin or an alloy of tin and bismuth but should have a meltingtemperature less than fusible material 16 and preferably less than about200° C. During the joining of the first component 10 to the secondcomponent 12, fusible material 16 must not melt so fusible material 24should have a melting point much lower than that of fusible material 16so that joining of the two components 10, 12 can be accomplished at atemperature less than the melting temperature of fusible material 16.Thus, the alloy of lead and tin should preferably be a eutectic alloy(melting point about 183° C.) while the alloy of tin and bismuth shouldalso be a eutectic alloy (melting point about 139° C.). Indium has amelting point of 156° C. While tin has a melting point of 232° C., it isacceptable for use in the present invention if a reflow temperature ofabout 250° C. can be tolerated.

Fusible material 24 is smaller in volume than fusible material 16. Thevolume of fusible material 24 should be just large enough to accomplishelectrical testing and burn-in while also mechanically anchoring thefirst component 10 to the second component 12. It is also advantageousto keep the volume of fusible material 24 as small as possible so as tofacilitate removal of first component 10 from second component 12without damaging fusible material 16. The present inventors have foundthat the volume of fusible material 24 should be about 5 to 20% of thevolume of fusible material 16. Qualitatively, it can be appreciated thatthe volume of fusible material 24 is substantially less than the volumeof fusible material 16.

For example, for a typical first component 10 having joining pads (notshown) of 5 mils in diameter and a 10 mil pitch (center to center ofadjoining pads), the volume of the fusible material 16 is about 76 cubicmils. The dimensions of the quantity of fusible material 24 depositedwould be about 2 to 3 mils in diameter and 1 to 2 mils in height,resulting in a volume of fusible material 24 of 3.14 to 14.2 cubic mils.Then, comparing the respective volumes of the fusible materials 16, 24,it can be seen that the volume of fusible material 24 is 4 to 18.6% ofthe volume of fusible material 16.

Fusible material 24 may be deposited by any conventional processincluding, but not limited to, screening of fusible material paste,micro-dispense of molten fusible material drops, decal transfer processor a photolithographic process.

The first component 10 and second component 12 can be separated by anyconventional process including, but not limited to, cold shear of thefirst component 10 off of the second component 12, hot shear (forexample, in a belt furnace at a temperature less than the solidus offusible material 16 but greater than the liquidus of fusible material24), hot tensile pull or hot vacuum removal.

Further, the bias temperature between the first and second components10, 12 can be modified for the hot removal options to optimize theremoval of the first component 10 from the second component 12. Forexample, the second component 12 can be separately heated or nitrogencan be directed at the first component 10 while in the furnace to coolthe first component 10, thereby increasing the temperature differencebetween the first component 10 and second component 12. In this manner,the lower melting fusible material 24 will remain mostly on the secondcomponent 12 and the fusible material ball 16 will be relativelyunaffected.

As another alternative, fusible material 24 may be kept in a moltenstate after joining and during electrical testing and burn-in. While thefusible material 24 is still molten, the first and second components 10,12 may be easily separated with minimal contamination of, or damage to,fusible material 16.

By controlling the amount of fusible material 24 and the removalconditions as just described, the integrity of the fusible material ball16 can be assured to be satisfactory for when the first component 10 ispermanently joined to its carrier. This is especially the case in thepresent invention since fusible material ball 16 never has to bereflowed.

After removal of the first component 10 from the second component 12,the second component 12 can be reused many times. If the volume offusible material 24 remaining on the second component 12 is sufficient,the second component 12 may be reused as is. If the volume of fusiblematerial 24 is insufficient, additional fusible material 24 may beadded. After some number of uses, second component 12 will have to bereworked which can be accomplished by removing any residual fusiblematerial 24 (such as by a vacuum pencil or a porous copper block) andthen redepositing the required amount of fusible material 24.

Referring now to FIG. 2, the second embodiment of the present inventionwill now be discussed. First component 10 and second component 12 ofFIG. 2 are identical to first component 10 and second component 12 asdiscussed previously with respect to FIG. 1 except that reduced area pad22 is no longer present in second component 12. Typical via size, suchas via 20 in FIG. 1, is about 5 to 6 mils in diameter. However, thepresent inventors have found that if the via size is reduced to 2 to 3mils, as is the case with via 20 in FIG. 2, reduced area pad 22 may bedispensed with. In this case, fusible material 24 is deposited directlyon via 20 as shown in FIG. 2.

It will be apparent to those skilled in the art having regard to thisdisclosure that other modifications of this invention beyond thoseembodiments specifically described here may be made without departingfrom the spirit of the invention. Accordingly, such modifications areconsidered within the scope of the invention as limited solely by theappended claims.

What is claimed is:
 1. A method of temporarily attaching a firstcomponent to a second component, the method comprising the steps of:preparing a first component having a first volume of fusible material;preparing a second component having a second quantity of fusiblematerial, wherein the first volume of fusible material has a meltingpoint higher than a melting point of the second volume of fusiblematerial and wherein the second volume of fusible material is 5 to 20%of the first volume of fusible material; joining the first and secondcomponents through the first and second volumes of fusible materialwithout melting of the first volume of fusible material.
 2. The methodof claim 1 further comprising the step of electrically testing andburning-in the first component after the step of joining.
 3. The methodof claim 1 further comprising the step of separating the first andsecond components after the step of joining.
 4. The method of claim 3wherein the step of separating is by cold shear, hot shear or hottensile pull.
 5. The method of claim 1 wherein the second volume offusible material is maintained in a molten state after joining andfurther comprising the step of separating the first and secondcomponents after the step of joining.
 6. The method of claim 1 whereinthe first component is a semiconductor device and the second componentis an electronic component.
 7. The method of claim 1 wherein the firstvolume of fusible material is a lead/tin alloy.
 8. The method of claim 1wherein the second volume of fusible material is selected from the groupconsisting of tin, indium, alloys of lead and tin, and alloys of tin andbismuth.
 9. The method of claim 1 wherein the second component has a viaand the second volume of fusible material is bonded directly to the via.10. The method of claim 1 wherein the second component has a via and apad on the via where the pad is smaller in cross-sectional area than thevia and the second volume of fusible material is bonded directly to thepad.
 11. A method of temporarily attaching a first component to a secondcomponent, the method comprising the steps of: preparing a firstcomponent having a first volume of fusible material; preparing a secondcomponent having a second volume of fusible material, wherein the firstvolume of fusible material has a melting point higher than a meltingpoint of the second volume of fusible material and wherein the secondvolume of fusible material is 5 to 20% of the first volume of fusiblematerial; joining the first and second components through the first andsecond volumes of fusible material without melting of the first volumeof fusible material; electrically testing and burning-in the firstcomponent; and separating the first and second components.
 12. Themethod of claim 11 wherein the step of separating is by cold shear, hotshear or hot tensile pull.
 13. The method of claim 11 wherein the secondvolume of fusible material is maintained in a molten state after joiningand during the, steps of electrically testing and burning-in andseparating.
 14. The method of claim 11 wherein the first component is asemiconductor device and the second component is an electroniccomponent.
 15. The method of claim 11 wherein the first volume offusible material is a lead/tin alloy.
 16. The method of claim 11 whereinthe second volume of fusible material is selected from the groupconsisting of tin, indium, alloys of lead and tin, and alloys of tin andbismuth.
 17. The method of claim 11 wherein the second component has avia and the second volume of fusible material is bonded directly to thevia.
 18. The method of claim 11 wherein the second component has a viaand a pad on the via where the pad is smaller in cross-sectional areathan the via and the second volume of fusible material is bondeddirectly to the pad.